L-Selegiline is a monoamine oxidase (MAO) inhibitor that was developed for the treatment of neurological disorders and is primarily used to treat Parkinson's disease. MAO is an enzyme responsible for metabolizing biogenic monoamines including serotonin, dopamine, histamine, and phenylethylamine. By inhibiting MAO located in the central nervous system (CNS), MAO inhibitors and their analogues increase the concentration of monoamines present within the brain synapses. This enhances monoamine-mediated neurotransmission, effectively treating neurological disorders such as Parkinson's disease and depression.
MAO enzymes are also located in a number of peripheral (non-CNS) tissues, including adipocytes, the cells that comprise body fat. The function of MAO enzymes in adipocytes has not been established. Currently, the only approved clinical use of L-selegiline and other MAO inhibitors is for the treatment of neurological disorders such as Parkinson's disease and depression.
Obesity is associated with an increase in the overall amount of adipose tissue (i.e., body fat), especially adipose tissue localized in the abdominal area. Obesity has reached epidemic proportions in the United States. The prevalence of obesity has steadily increased over the years among all racial and ethnic groups. According to the United States Surgeon General, 61% of the adult population and 14% of children are obese or overweight. Forty four million Americans are obese, with an additional eighty million deemed medically overweight. Obesity is responsible for more than 300,000 deaths annually, and will soon overtake tobacco usage as the primary cause of preventable death in the United States. Obesity is a chronic disease that contributes directly to numerous dangerous co-morbidities, including type 2 diabetes, cardiovascular disease, inflammatory diseases, premature aging, and some forms of cancer. Type 2 diabetes, a serious and life-threatening disorder with growing prevalence in both adult and childhood populations, is currently the 7th leading cause of death in the United States. Since more than 80% of patients with type 2 diabetes are overweight, obesity is the greatest risk factor for developing type 2 diabetes. Increasing clinical evidence indicates that the best way to control type 2 diabetes is to reduce weight.
The most popular over-the counter drugs for the treatment of obesity, phenylpropanolamine and ephedrine, and the most popular prescription drug, fenfluramine, were removed from the marketplace as a result of safety concerns. Drugs currently approved for the long-term treatment of obesity fall into two categories: (a) Central Nervous System (CNS) appetite suppressants such as sibutramine and (b) gut lipase inhibitors such as orlistat. CNS appetite suppressants reduce eating behavior through activation of the ‘satiety center’ in the brain and/or by inhibition of the ‘hunger center’ in the brain. Gut lipase inhibitors reduce the absorption of dietary fat from the gastrointestinal (GI) tract. Although sibutramine and orlistat work through very different mechanisms, they share in common the same overall goal of reducing body weight secondary to reducing the amount of calories that reach the systemic circulation. Unfortunately, these indirect therapies produce only a modest initial weight loss (approximately 5% compared to approximately 2% with placebo) that is usually not maintained. After one or two years of treatment, most patients return to or exceed their starting weight. In addition, most approved anti-obesity therapeutics produce undesirable and often dangerous side effects that can complicate treatment and interfere with a patient's quality of life.
The lack of therapeutic effectiveness, coupled with the spiraling obesity epidemic, positions the ‘treatment of obesity’ as one of the largest and most urgent unmet medical needs. There is, therefore, a real and continuing need for the development of improved medications that treat or prevent obesity.
General MAO-B inhibitors such as selegiline have been clinically useful in the treatment of CNS disorders. They have now unexpectedly been discovered to also have anti-obesity activity. Even more surprising is that the anti-obesity activity mediated by these agents is outside of the CNS. This new discovery provides a novel approach for the prevention or treatment of obesity. Moreover, if the CNS effects of these compounds can be eliminated, their peripherally mediated anti-obesity properties should provide therapeutic agents with greater safety. It has, as a result, become highly desirable to find MAO-B inhibitors with limited or no CNS effects. Compounds of this sort are expected to be useful in treating obesity and the variety of co-morbidities to which it contributes.